The present application claims priority from U.S. provisional application Ser. No. 60/004,640, filed Sep. 29, 1995.
The present invention relates to a comparator circuit for comparing a negative input voltage signal with a positive input voltage signal.
Generally, negative voltages may not be applied to integrated circuits which have single positive voltage power supplies because parasitic diode elements of the integrated circuitry may not have negative potentials applied to them with respect to the substrate of the integrated circuit. Reverse biasing of these circuit elements would lead to latch-up and ultimately to the failure of the integrated circuit.
When a circuit application requires the comparison of a negative signal voltage against a threshold level set by a positive reference, implementation of a comparator circuit on a single integrated circuit has necessitated bipolar power supplies with positive and negative supply voltages applied to the integrated circuit. In this manner, it can be ensured that no point in the circuitry is more negative than the substrate of the integrated circuit. This solution entails the expense and complexity of a dual voltage power supply.
An alternative method of comparing negative voltage signals with a positive reference voltage requires the inversion of the negative voltage signal with respect to ground by using components external to the integrated circuit. Again, a penalty is incurred in circuit complexity.